In a rack mount device or a disk array device, a unit that stores a plurality of memory devices, for example, hard disk devices (hereinafter, referred to as HDDs) in a housing is withdrawably installed in a rack. Such devices are used as a storage device in a data center. Since a large amount of data is exchanged in such data center, there is a demand for an increased number of HDD allowed to be installed in one rack, for example, increased capacity per unit installation area.
Related techniques are disclosed in Japanese Laid-open Patent Publication Nos. 2007-4538 and 2004-22059.